Movie film is designed for repetitive use and, as such, must be durable and true to its original shape and size over a long period of time. Curling, cracking or peeling of the film is not tolerable. In addition, the film must be kept clean from skin oils, dust and other matter which can be deposited during film processing and handling. It is generally necessary to clean movie film several times during its life. Cleaning is conveniently done by immersing the film in a solvent which may be contemporaneously subjected to sonication. The solvent is contained in a tank and the film is fed through the tank via film guides. The film is dried as it is removed from the tank and is rewound. The solvent must be capable of cleaning the film without leaving a deposit on the film and without causing any distortion or damage to the film.
Heretofore, a preferred solvent has been 1,1,1-trichloroethane. However, this solvent is no longer favored due to environmental concerns. Alkyl bromide solvents, and especially n-propyl bromide, are environmentally acceptable but may cause film damage and so must be used in combination with co-solvents (see U.S. Pat. Nos. 5,665,173, 5,669,985, and 5,679,632).
The addition of small amounts of no more than about 5% by volume of a fluorine and/or chlorine containing brominated hydrocarbon, such as dibromodifluoromethane, to a flammable organic solvent to provide a fire retardant solvent composition is disclosed in U.S. Pat. No. 5,207,953. A hot vapor stripping process for removing resin coatings from paperstock, which uses an acyclic hydrocarbon containing one to three carbons and two to eight bromine, chlorine or fluorine atoms, at least two of which are bromine or chlorine, is described in U.S. Pat. No. 4,193,838. Solvents such as bromochloromethanes have been disclosed for use in various equipment cleaning operations (for example see U.S. Pat. Nos. 3,773,677 and 4,056,403).
A film cleaning process has now been found which uses environmentally friendly alkyl brominated solvents which do not require the presence of co-solvents in order to avoid film damage. The solvents include at least one other halogen atom chosen from chlorine and fluorine.